- Email: [email protected]
A new design for amorpphous core distribution transformer
Materials Science and Engineering, 99 (1988) 19-21
19
A New Design for Amorphous Core Distribution Transformer* R. SCHULZ, N. CHRETIEN, N. ALEXANDROV, J. AUBIN and R. ROBERGE
Hydro-Qubbec, Vice presidence recherche (IREQ), 1800 Montbe Ste-Julie, Varennes, Qubbec, JOL 2PO (Canada)
Abstract
A new design and a pre-prototype 2 5 k V A amorphous-core dry distribution transformer under development at Hydro-Qubbec are described and compared with other designs. The power capacity o f the transformer can easily be doubled by internal cooling. 1. Introduction
Among all the possible core-coil configuration for distribution transformers only a few are adequate for amorphous-core transformers because of the particular nature of amorphous metal ribbons. The small thickness of the ribbon, the lower saturation induction, the hardness, the relative brittleness after heat treatment and the high magnetostriction (i.e. influence of stress on core loss) are all important factors in determining an optimal design and the best manufacturing procedure. The six most suitable configurations, listed under three assembly options, are shown in Fig. I [1]. In assembly options I and II, the coil is wound around a previously annealed wound core while assembly option III consists of winding preannealed amorphous metal into a previously formed coil. Most of the transformer manufacturers have, so far, developed amorphous-core prototypes involving assembly options I and II. Table 1 shows a partial list of companies and utilities involved in the manufacturing of amorphous distribution transformers. Assembly option III was discarded by several transformer designers [2] because of the general belief that if the core is not annealed after forming, it would have unacceptable losses. This paper reports the successful fabrication of a 25 kVA low-loss amorphous-core dry distribution transformer prototype using configuration IliA and gives preliminary test results. 2. Design considerations
Figure 2 illustrates a schematic of the transformer design. This configuration presents several advan*Paper presented at the Sixth International Conference on Rapidly Quenched Metals, Montr6al, August 3-7, 1987. 0025-5416/88/$3.50
tages. First it is possible to use ribbons with very large width in contrast with configuration IA or IB which have cruciform-type core and therefore need either ribbons of varying width or at least much narrower ribbons in order to fill efficiently the circular coil opening. Second the core does not have to support the whole assembly as in core type configurations IA and liB and therefore simple and light core support can be used. There are no sharp corners or portions of the core with small radius of curvature as in IA, IB and liB where stress concentration can give rise to local plastic deformation during annealing. The magnetoelastic strain introduced during core annealing is known to contribute significantly to the total loss [3]. The core geometry in configuration I l i a allows straightforward application of the technique of flash heating [4] or dynamic annealing recently proposed in the literature [5]. This design offers great advantages in manufacturing techniques compared with other designs such as configuration IIA which require a toroidal winding technique and are therefore complex and expensive procedures. Finally, since the coil is formed first, this configuration is the most adequate for dry transformer design where the electrical circuit is molded in an epoxy resin. 3. Manufacturing details
The construction of the prototype begins with the coil assembly. The primary winding, located in the center, consists of 1084 turns of 2 mm x 2 mm copper strips. The secondary windings are stacked on each side of the primary winding and are made with copper strips of different cross-sections (average value 2 mm x 120 mm) in order to form a circular cross-section. The number of turns on the secondary is 19 and they are isolated from each other by Nomex paper. A cooling coil is soldered on the secondary winding at some strategic locations. The electrical circuit thus assembled is molded under vacuum in an epoxy resin (155 °C class). The heat treatment of the Metglas (2605-$2) amorphous ribbon is achieved in a specially designed oven and heat treated at 360 °C for 2 h under inert gas. The heat is applied in the axial core direction to ensure a homogeneous temperature © Elsevier Sequoia/Printed in The Netherlands
2O TABLE 1 Partial list of participants in the development of distribution transformer
Company
Capacity (kVA)
Core loss (W)
Copperloss (W)
Allied-Signal Inc. (U.S.A.)
15 25 50
14 16 28
166 -422
General Electric (U.S.A.)
25 25 50
28 18 30
-330 455
10 25 25 500
11 29 20 --
-----
Westinghouse (U.S.A.)
Osaka Transformers (Japan)
10 30
8.6 30.0
McGraw-Edison (U.S.A.)
10 25
7.6 15
Tokaoka Electrical (Japan)
20
18.9
Mitsubishi Electrical (Japan)
35
49
98
100
85
1780
12.1
--
Toshiba (Japan) GEC
16
A
I
1
173 390 --348
Fig. 2. Schematic diagram of the IREQ transformer design.
(U.K.)
Other participants in the field are ASEA (Sweden), RTE (U.S.A.), Kuhlman (U.S.A.), Sanyo Special Steel (Japan), Nippon Steel (Japan), Tokoku Metal (Japan), Central Moloney (U.S.A.), Kansai Electrical (Japan), Shanghai Transformers (China).
d i s t r i b u t i o n . A f t e r h e a t t r e a t m e n t the r i b b o n is w o u n d in its final p o s i t i o n a r o u n d the legs o f the electrical coil. T h e t e c h n i q u e used allows the r e l a x a t i o n o f the i n n e r m o s t p o r t i o n o f w o u n d c o r e s w h i c h are k n o w n to c o n t r i b u t e significantly to the total core losses [3] at
I
II
"aT
#Indlng lhe coil orcund on unj0inWd Windinglhe coil Oroundonungirded WindinQl~lOnneelod omoqphow I~ c~(e by ull~ I o ~ l Illllal ollkl 0 pl'ivlooliy li~md coil I~lnd ~ e ~ (Gl°tlll Ihl ~1 WllldinQnlll h~l$ ~ rGlotlni I l l ~ w~mO (A)
G£C-ostutA design
onMing (A)
w~m~ ALLI~doS~
~ (A)
omo(~mm mttm wimlin IRF.a ~ s ~ A Cote
A
TABLE 2 Major characteristics of Hydro-Quebec 25 kVA pre-prototype dry transformer Power rating With no internal cooling With 4 cm 3 s - t cooling flow Voltage rating
25 kVA 50 kVA 6.56 kV/115 V
Electrical circuit molded in epoxy resin ( 155 °C class) Seclion A-A Toroidol-ty~l
~ A-A Core-t~ (wound coil)
(8)
G( -(PRI Ue~ln ¢o(e
Shell -ty~l (wotundcole)
(a)
(B) Co~
Number of primary turns Number of secondary turns
Coil
Seclm A-A Shill-t)~e (l~und coil)
Fig. I. Possible core-coil configurations and various assembly options for amorphous core distribution transformers.
1084 19
Internal cooling by copper tubes fixed on the secondary winding Total weight
200 kg
Weight of amorphous metal
76.2 kg
Core loss at 1.3 T and 22 °C
18.5 W
Copper loss at 25 kVA at 52 kVA High-voltage winding resistance
300 W 1230 W 25 f2
21 the expense of a slight increase (no more than 5%) in the core space factor. 4. Test results
Table 2 gives the general characteristics of the 25 kVA pre-prototype under development at HydroQuebec and Fig. 3 shows a picture of the transformer. The equilibrium temperature of the primary and secondary winding for various primary currents and cooling conditions are shown in Table 3. It should be noticed that with a cooling flow a r i o w as 4 c m 3 s l, it is possible to double the nominal power capacity of the transformer keeping the raising temperature below 110 °C. For a primary current of 10 A a large difference in the temperature between the primary and secondary windings is observed at 15 cm 3 s-~ arising from the fact that the cooling coil is not in direct contact with the high-voltage winding. 5. Conclusion
Fig. 3. Pre-prototype 25 kVA dry transformer built at IREQ.
A low-loss amorphous-core dry distribution transformer has been fabricated. The design does not require core post-annealing and is therefore very easy to manufacture. The core losses are comparable with or less than other designs. The core space factor is approximately 5% less than the value usually reported in the literature. With internal cooling we can easily double and almost triple the nominal power capacity of the transformer. The prototype can handle 100% overcharge with only a 4 cm 3 s-1 cooling flow.
TABLE 3 Equilibriumtemperatureof the low- and high-voltage windings for various primarycurrents and cooling conditions
Acknowledgment
Cooling flow
The authors wish to acknowledge Gr~goire Par~ for his technical assistance.
27.3 k VA
52.5 k VA
65.6 k VA
Primary current
Primary current
Primary current
4.163 A LV 109 HV 119
8.0 A
10 A
LV HV LV HV
LV 82.7 HV 149
(cm3 s- ')
0 4 15
LV 26.3 HV 33.3
72.9 110 56.8 92.7
LV, low-voltage winding; HV, high-voltage winding. Temperature in degrees Celsius above ambient.
References
1 R. Schulz, N. Alexandrov and R. Roberge, CIGRE Symp. on New and Improved Materials for Electrotechnology, Vienna, May, Cigr6 Symposium No. S 05-87, Paris, 1987,pp. 300-305. 2 E. L. Boyd and J. D. Borst, 1EEE Trans. Power Appar. Syst., 103 (1984) 3365. 3 D. M. Nathasingh and H. Liebermann, Transformer Applications of Amorphous Alloys in Power Distribution Systems, 1EEE Transactions on Power Delivery, Vol. PWRD-2, No. 3,
July 1987, pp. 843-850. 4 A. I. Taub, J. Appl. Phys., 55(1984) 1775. 5 A. I. Taub, IEEE Trans. Magn., 20(1984) 564.
19
A New Design for Amorphous Core Distribution Transformer* R. SCHULZ, N. CHRETIEN, N. ALEXANDROV, J. AUBIN and R. ROBERGE
Hydro-Qubbec, Vice presidence recherche (IREQ), 1800 Montbe Ste-Julie, Varennes, Qubbec, JOL 2PO (Canada)
Abstract
A new design and a pre-prototype 2 5 k V A amorphous-core dry distribution transformer under development at Hydro-Qubbec are described and compared with other designs. The power capacity o f the transformer can easily be doubled by internal cooling. 1. Introduction
Among all the possible core-coil configuration for distribution transformers only a few are adequate for amorphous-core transformers because of the particular nature of amorphous metal ribbons. The small thickness of the ribbon, the lower saturation induction, the hardness, the relative brittleness after heat treatment and the high magnetostriction (i.e. influence of stress on core loss) are all important factors in determining an optimal design and the best manufacturing procedure. The six most suitable configurations, listed under three assembly options, are shown in Fig. I [1]. In assembly options I and II, the coil is wound around a previously annealed wound core while assembly option III consists of winding preannealed amorphous metal into a previously formed coil. Most of the transformer manufacturers have, so far, developed amorphous-core prototypes involving assembly options I and II. Table 1 shows a partial list of companies and utilities involved in the manufacturing of amorphous distribution transformers. Assembly option III was discarded by several transformer designers [2] because of the general belief that if the core is not annealed after forming, it would have unacceptable losses. This paper reports the successful fabrication of a 25 kVA low-loss amorphous-core dry distribution transformer prototype using configuration IliA and gives preliminary test results. 2. Design considerations
Figure 2 illustrates a schematic of the transformer design. This configuration presents several advan*Paper presented at the Sixth International Conference on Rapidly Quenched Metals, Montr6al, August 3-7, 1987. 0025-5416/88/$3.50
tages. First it is possible to use ribbons with very large width in contrast with configuration IA or IB which have cruciform-type core and therefore need either ribbons of varying width or at least much narrower ribbons in order to fill efficiently the circular coil opening. Second the core does not have to support the whole assembly as in core type configurations IA and liB and therefore simple and light core support can be used. There are no sharp corners or portions of the core with small radius of curvature as in IA, IB and liB where stress concentration can give rise to local plastic deformation during annealing. The magnetoelastic strain introduced during core annealing is known to contribute significantly to the total loss [3]. The core geometry in configuration I l i a allows straightforward application of the technique of flash heating [4] or dynamic annealing recently proposed in the literature [5]. This design offers great advantages in manufacturing techniques compared with other designs such as configuration IIA which require a toroidal winding technique and are therefore complex and expensive procedures. Finally, since the coil is formed first, this configuration is the most adequate for dry transformer design where the electrical circuit is molded in an epoxy resin. 3. Manufacturing details
The construction of the prototype begins with the coil assembly. The primary winding, located in the center, consists of 1084 turns of 2 mm x 2 mm copper strips. The secondary windings are stacked on each side of the primary winding and are made with copper strips of different cross-sections (average value 2 mm x 120 mm) in order to form a circular cross-section. The number of turns on the secondary is 19 and they are isolated from each other by Nomex paper. A cooling coil is soldered on the secondary winding at some strategic locations. The electrical circuit thus assembled is molded under vacuum in an epoxy resin (155 °C class). The heat treatment of the Metglas (2605-$2) amorphous ribbon is achieved in a specially designed oven and heat treated at 360 °C for 2 h under inert gas. The heat is applied in the axial core direction to ensure a homogeneous temperature © Elsevier Sequoia/Printed in The Netherlands
2O TABLE 1 Partial list of participants in the development of distribution transformer
Company
Capacity (kVA)
Core loss (W)
Copperloss (W)
Allied-Signal Inc. (U.S.A.)
15 25 50
14 16 28
166 -422
General Electric (U.S.A.)
25 25 50
28 18 30
-330 455
10 25 25 500
11 29 20 --
-----
Westinghouse (U.S.A.)
Osaka Transformers (Japan)
10 30
8.6 30.0
McGraw-Edison (U.S.A.)
10 25
7.6 15
Tokaoka Electrical (Japan)
20
18.9
Mitsubishi Electrical (Japan)
35
49
98
100
85
1780
12.1
--
Toshiba (Japan) GEC
16
A
I
1
173 390 --348
Fig. 2. Schematic diagram of the IREQ transformer design.
(U.K.)
Other participants in the field are ASEA (Sweden), RTE (U.S.A.), Kuhlman (U.S.A.), Sanyo Special Steel (Japan), Nippon Steel (Japan), Tokoku Metal (Japan), Central Moloney (U.S.A.), Kansai Electrical (Japan), Shanghai Transformers (China).
d i s t r i b u t i o n . A f t e r h e a t t r e a t m e n t the r i b b o n is w o u n d in its final p o s i t i o n a r o u n d the legs o f the electrical coil. T h e t e c h n i q u e used allows the r e l a x a t i o n o f the i n n e r m o s t p o r t i o n o f w o u n d c o r e s w h i c h are k n o w n to c o n t r i b u t e significantly to the total core losses [3] at
I
II
"aT
#Indlng lhe coil orcund on unj0inWd Windinglhe coil Oroundonungirded WindinQl~lOnneelod omoqphow I~ c~(e by ull~ I o ~ l Illllal ollkl 0 pl'ivlooliy li~md coil I~lnd ~ e ~ (Gl°tlll Ihl ~1 WllldinQnlll h~l$ ~ rGlotlni I l l ~ w~mO (A)
G£C-ostutA design
onMing (A)
w~m~ ALLI~doS~
~ (A)
omo(~mm mttm wimlin IRF.a ~ s ~ A Cote
A
TABLE 2 Major characteristics of Hydro-Quebec 25 kVA pre-prototype dry transformer Power rating With no internal cooling With 4 cm 3 s - t cooling flow Voltage rating
25 kVA 50 kVA 6.56 kV/115 V
Electrical circuit molded in epoxy resin ( 155 °C class) Seclion A-A Toroidol-ty~l
~ A-A Core-t~ (wound coil)
(8)
G( -(PRI Ue~ln ¢o(e
Shell -ty~l (wotundcole)
(a)
(B) Co~
Number of primary turns Number of secondary turns
Coil
Seclm A-A Shill-t)~e (l~und coil)
Fig. I. Possible core-coil configurations and various assembly options for amorphous core distribution transformers.
1084 19
Internal cooling by copper tubes fixed on the secondary winding Total weight
200 kg
Weight of amorphous metal
76.2 kg
Core loss at 1.3 T and 22 °C
18.5 W
Copper loss at 25 kVA at 52 kVA High-voltage winding resistance
300 W 1230 W 25 f2
21 the expense of a slight increase (no more than 5%) in the core space factor. 4. Test results
Table 2 gives the general characteristics of the 25 kVA pre-prototype under development at HydroQuebec and Fig. 3 shows a picture of the transformer. The equilibrium temperature of the primary and secondary winding for various primary currents and cooling conditions are shown in Table 3. It should be noticed that with a cooling flow a r i o w as 4 c m 3 s l, it is possible to double the nominal power capacity of the transformer keeping the raising temperature below 110 °C. For a primary current of 10 A a large difference in the temperature between the primary and secondary windings is observed at 15 cm 3 s-~ arising from the fact that the cooling coil is not in direct contact with the high-voltage winding. 5. Conclusion
Fig. 3. Pre-prototype 25 kVA dry transformer built at IREQ.
A low-loss amorphous-core dry distribution transformer has been fabricated. The design does not require core post-annealing and is therefore very easy to manufacture. The core losses are comparable with or less than other designs. The core space factor is approximately 5% less than the value usually reported in the literature. With internal cooling we can easily double and almost triple the nominal power capacity of the transformer. The prototype can handle 100% overcharge with only a 4 cm 3 s-1 cooling flow.
TABLE 3 Equilibriumtemperatureof the low- and high-voltage windings for various primarycurrents and cooling conditions
Acknowledgment
Cooling flow
The authors wish to acknowledge Gr~goire Par~ for his technical assistance.
27.3 k VA
52.5 k VA
65.6 k VA
Primary current
Primary current
Primary current
4.163 A LV 109 HV 119
8.0 A
10 A
LV HV LV HV
LV 82.7 HV 149
(cm3 s- ')
0 4 15
LV 26.3 HV 33.3
72.9 110 56.8 92.7
LV, low-voltage winding; HV, high-voltage winding. Temperature in degrees Celsius above ambient.
References
1 R. Schulz, N. Alexandrov and R. Roberge, CIGRE Symp. on New and Improved Materials for Electrotechnology, Vienna, May, Cigr6 Symposium No. S 05-87, Paris, 1987,pp. 300-305. 2 E. L. Boyd and J. D. Borst, 1EEE Trans. Power Appar. Syst., 103 (1984) 3365. 3 D. M. Nathasingh and H. Liebermann, Transformer Applications of Amorphous Alloys in Power Distribution Systems, 1EEE Transactions on Power Delivery, Vol. PWRD-2, No. 3,
July 1987, pp. 843-850. 4 A. I. Taub, J. Appl. Phys., 55(1984) 1775. 5 A. I. Taub, IEEE Trans. Magn., 20(1984) 564.